This invention relates generally to x-ray tubes, and more particularly to x-ray tube bearing assemblies.
X-ray equipment used in for diagnostic imaging typically includes a rotating anode x-ray tube. Such x-ray tubes are vacuum tubes, each including a rotatable shaft and a stator which circumferentially surrounds, or is circumferentially surrounded by, the rotatable shaft. A pair of bearings, such as rolling element bearings (e.g., ball bearings), are positioned radially between the shaft and the stator. An x-ray target, which typically is attached to the rotatable shaft, is heated to high temperatures by impinging electrons emitted by the cathode. The bearings are poor thermal conductors, commonly resulting in a temperature differential between the shaft side and the stator side of the bearings causing misalignment and wear which limits the operating power of the x-ray tube. During high voltage operation, the bearings are prone to electrical arcing which is a disadvantage in designs requiring a stable electrical path between the shaft and the stator. Known designs include those which use liquid metal (such as Gallium or Gallium alloys) in the annularly-cylindrical gap between the shaft and the stator as a hydrodynamic bearing as well as to conduct heat and electricity. Such liquid metal equalizes the temperature on both sides of the bearing which increases bearing life; however, such designs are at risk of leakage of the liquid metal out of the gap with such escaped liquid metal causing electrical (high voltage) instability which shortens the operating life of the x-ray tube.
What is needed, for x-ray tubes employing liquid metal for thermal and/or electrical conduction purposes, is an improved x-ray tube design which prevents leakage of the liquid metal from the gap between the shaft and the stator.
The present invention provides, in one embodiment, a bearing assembly consisting of a rotatable shaft and a stator coaxially aligned. The stator has at least one circumferential protrusion that contains respective segments that extend radially from the stator. Each of the respective segments contains at least one capture cavity and has a main cavity disposed between each of the respective segments so as to house a thermal shunt. A plurality of roller bearings are also disposed radially between the rotatable shaft and the stator. In addition, at least one viscoseal is disposed on the rotatable shaft.